This chapter provides a brief overview of phase diagrams, explaining what they represent and how and why they are used. It identifies key points, lines, and features on a binary nickel-copper phase diagram and explains what they mean from a practical perspective. It also discusses the concept of equilibrium, the significance of Gibb’s phase rule, the theorem of Le Chatelier, and the use of the lever rule.

This chapter describes the physical characteristics, properties, and behaviors of solid solutions under equilibrium conditions. It begins with a review of a single-component pure metal system and its unary phase diagram. It then examines the solid solution formed by copper and nickel atoms. It discusses the difference between interstitial and substitutional solid solutions and the factors that determine the type of solution that two metals are likely to form. It also addresses the development of intermediate phases, the role of free energy, transformation kinetics, liquid-to-solid and solid-state phase transformations, and the allotropic nature of metals.

This chapter explains how the principles of chemical thermodynamics are used in the construction and interpretation of phase diagrams. After a brief review of the laws of thermodynamics, it describes the concept of Gibbs free energy and its application to transformations that occur in single-component and binary solid solutions. It then examines the relationship between the free energy of a solution and the chemical potentials of the individual components. It also explains how to account for the heat of mixing using quasi-chemical models, discusses the effect of interatomic bond energies and chemical potentials, and shows how the equilibrium state of an alloy can be obtained from free-energy curves.

This chapter discusses the unique characteristics of isomorphous alloy systems. It begins with a review of the naming conventions for multi-component systems and the construction of a three-dimensional phase diagram for a two-component alloy system. It explains how phase diagrams can be constructed from time-temperature cooling curves and how they can be used to predict the phases present, their chemical compositions, and relative amounts. It also shows how phase diagrams can be modified to account for nonequilibrium cooling conditions.

This chapter begins by presenting a generic eutectic phase diagram and identifying critical points, lines, and features. It then describes the composition and properties of aluminum-silicon and lead-tin eutectic systems, the characteristics of eutectic morphologies, the solidification and scale of eutectic structures, and the competitive growth of dendrites and eutectic colonies or cells. It also examines the different types of precipitation structures that form during slow cooling cycles.

This chapter discusses the phase transformations of peritectic alloy systems. It describes the processes involved with equilibrium and nonequilibrium freezing, the mechanisms of peritectic formation, and the resulting microstructures. It also discusses the formation of peritectic structures in iron-base alloys and multicomponent systems.

This chapter provides a brief overview of monotectic alloy systems and reactions. It begins by presenting a monotectic phase diagram and identifying important points, lines, and regions. It then describes the monotectic reactions that occur in copper-lead systems and the associated solidification structures. It also discusses the morphology of the microstructure produced during directional solidification and the classification criteria of low- and high-dome alloys.

This chapter discusses the characteristics of eutectoid transformations, a type of solid-state transformation associated with invariant reactions, focusing on the iron-carbon system of steel. It describes the compositions, characteristics, and properties of ferrite, eutectoid, hypoeutectoid, and hypereutectoid structures and how they are affected by the addition of various alloying elements. The chapter also discusses the formation of peritectoid structures in the uranium-silicon alloy system.

This chapter explains how the presence of intermediate phases affects the melting behavior of binary alloys and the transformations that occur under different rates of cooling. It begins by examining the phase diagrams of magnesium-lead and copper-zinc, noting some of the complexities associated with intermediate phases. It then discusses the difference between ordered and disordered phases and how they are accounted for on phase diagrams. It describes how the atoms in a disordered solution may arrange themselves into an ordered array, forming a superlattice in the process of cooling, and goes on to identify the most common superlattice structures and their corresponding alloy phases. It also discusses the factors that limit the formation of superlattices along with the kinetics of spinodal decomposition and its effect on microstructure development.

This chapter discusses the construction, interpretation, and use of ternary phase diagrams. It begins by examining a hypothetical phase space diagram and several corresponding two-dimensional plots. It then describes one of the most basic tools of metallurgy, the Gibbs triangle, and explains how to construct tie lines to analyze intermediate compositions and phases. It also discusses the use of three-dimensional temperature-composition diagrams, three- and four-phase equilibrium phase diagrams, and binary and ternary phase diagrams associated with the iron-chromium-nickel alloy system.

Gas-metal reactions can have a significant impact on metals and alloys, affecting their properties (during processing) and accelerating service failures, particularly in hot, corrosive environments. This chapter discusses the kinetics of gas-metal reactions and how they are driven by Gibbs energy changes. It plots the energy of formation for many important metal oxides and explains how to construct isothermal stability diagrams to analyze complex reactions involving metals, alloys, and gases containing more than one reactive component.

This chapter discusses some of the methods and measurements used to construct phase diagrams. It explains how cooling curves were widely used to determine phase boundaries, and how equilibrated alloys examined under controlled heating and cooling provide information for constructing isothermal and vertical sections as well as liquid projections. It also explains how diffusion couples provide a window into local equilibria and identifies typical phase diagram construction errors along with problems stemming from phase-boundary curvatures and congruent transformations.

This chapter provides an overview of a computational method, called CALPHAD, used for the study of phase equilibria in multicomponent systems. It describes the thermodynamic models and calculation techniques employed in the software and explains how it applies to complex alloys used in industry. It also provides examples showing how CALPHAD has been used to determine the formability of metallic glass, calculate the dilation of stainless steel during phase transformation, and predict the beta transus and approach curves of commercial titanium alloys.

This chapter discusses the use of phase diagrams in alloy design, processing, and performance assessment. The examples cover both ferrous and nonferrous metals and a variety of goals and objectives. The chapter also identifies limitations and pitfalls associated with the use of phase diagrams.

This chapter examines two important strengthening mechanisms, martensitic and bainitic transformations, both of which occur under nonequilibrium cooling conditions. It explains how time-temperature-transformation diagrams are constructed and how they are used to understand and control the formation of martensite and bainite in steel and other alloys. It describes the morphology of both types of structures, the factors that influence their formation, how they respond to tempering processes, and their effect on mechanical properties and behaviors. It also discusses the role of transformation hysteresis in shape memory alloys.

This chapter discusses the basic principles of precipitation hardening, an important strengthening mechanism in nonferrous alloys as well as stainless steel. It begins with a detailed review of the theory of precipitation hardening, then describes its application to aluminum alloys and nickel-base superalloys.

This appendix provides a detailed overview of the crystal structure of metals. It describes primary bonding mechanisms, space lattices and crystal systems, unit cell parameters, slip systems, and crystallographic planes and directions as well as plastic deformation mechanisms, crystalline imperfections, and the formation of surface or planar defects. It also discusses the use of X-ray diffraction for determining crystal structure.

The solidification process has a major influence on the microstructure and mechanical properties of metal casting as well as wrought products. This appendix covers the fundamentals of solidification. It discusses the formation of solidification structures, the characteristics of planar, cellular, and dendritic growth, the basic freezing sequence for an alloy casting, and the variations in cooling rate, heat flow, and grain morphology in different areas of the mold. It also describes the types of segregation that occur during freezing, the effect of solidification rate on secondary dendrite arm spacing, and the factors that contribute to porosity and shrinkage.